1. Field of the Invention
The present invention relates to a semiconductor luminescent device having an organic/inorganic junction structure.
2. Description of the Related Art
In recent years, research and development of an organic electro luminescent device to be used as, e.g., a display device or an illumination device have become a big concern. For example, Shogo Saito at Kyushu University has reported a organic two-layered structure device using metal electrode/aromatic dye/polythiophene/transparent electrode in 1986 (J.J. Appl. Phys. 25, L773, 1986). In this device, the thickness of an organic film is 1 .mu.m or more, and an application voltage is as high as 100 V. C. W. Tang et al. of Eastman Kodak Co. have reported that when the thickness of an organic film is decreased to be 1,000 .ANG. or less in an organic two-layered structure of Mg.multidot.Ag/Alq3/diamine/ITO, a device using this structure can provide a practically satisfactory luminosity when it is driven at an application voltage of 10 V or less (Appl. Phys. Lett., 51 (12), 21 Sept. 1987, pp. 913-915) . These luminescent devices are based on an organic two-layered structure obtained by combining a dye having an electron injecting property and a dye having a hole injecting property and have characteristic features in that the thickness of an organic film is minimized, a material having a small work function is selected as a metal electrode on an electron injection side, and a material is selected so as not to produce an electrical defect when an organic film is formed by a vacuum deposition method or a sublimation method. Shogo Saito at Kyushu University has further proposed an organic three-layered structure device of electron-injecting layer/luminescent layer/hole-injecting layer and reported that high-luminosity luminescence can be obtained by selecting a dye having high photoluminescence as a luminescent layer (J.J. Appl. Phys., 27, L269, 1988).
In addition, many researches efforts such as research into luminescent device structure obtained by combining various types of organic films, research indicating that a certain degree of luminescence can be obtained even in a single-layered organic film by mixing a luminescent agent and a hole injecting agent, and research concerning characteristic degradation in Alq3 as a luminophor have been reported, and a large number of associated patent applications have been filed.
In a flat display panel which has been used in various types of electronic equipment in recent years, a large number of display pixels are arranged in a matrix manner and time-divisionally driven. The flat panel display system is classified into a simple matrix system and an active matrix system. In each system, however, a drive voltage to be applied on one pixel is pulsated, and a voltage application time is very short. In order to obtain an image with high quality, therefore, each pixel must have a certain degree of memory function. In a liquid-crystal display, for example, this memory function is obtained by the capacitance of a liquid crystal itself or a capacitance connected in parallel with the liquid crystal.
Similarly, an organic film luminescent device must have the memory function when it is applied to the matrix-driven flat panel display as described above. No organic film luminescent device having such a memory function, however, has been reported yet.
In addition, the life of a luminescent device using an organic film is very short, i.e., about 1,000 hours. This is mainly because the luminous efficacy of the device is as low as at most about 1% and Joule heat is generated by current components not contributing to luminescence and destroys an organic film structure which is weak against heat.
As described above, an organic film luminescent device is still far from the stage of practical applications in terms of characteristics and lifetime.